Malacostraca

Malacostraca is the largest of the six classes of crustaceans, containing about 40,000 living species, divided among 16 orders. Its members, the malacostracans, display a great diversity of body forms and include crabs, lobsters, crayfish, shrimp, krill, woodlice, amphipods, mantis shrimp and many other, less familiar animals. They are abundant in all marine environments and have colonised freshwater and terrestrial habitats. They are segmented animals, united by a common body plan comprising 20 body segments (rarely 21), and divided into a head, thorax, and abdomen.

Characteristics

The body of a malacostracan is divided into 20 segments, which are grouped into three regions: the cephalon (head), the pereon (thorax) and the pleon (abdomen). Each segment bears a pair of appendages, although these may be lost or modified. In most species, the body is laterally compressed, with the segments and appendages generally reduced in size to decrease weight.

Classification

The class Malacostraca includes about 40,000 species, and "arguably... contains a greater diversity of body forms than any other class in the animal kingdom". Malacostracans have abdominal appendages, a fact that differentiates them from all other crustaceans. They also have a thorax differentiated into maxilliped and pereopod-bearing segments, a carapace covering at least some of the thorax, and stalked eyes.

Ecology

Malacostracans are found in a variety of habitats all over the world, from the deep sea to mountain streams, and in all continents. They are particularly common in coastal and marine environments, where they can form large parts of the benthic biomass and play important roles in the ecology.

See also

• Crustacean
• Arthropod

References

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